This invention relates to high power (nonlinear) testing of radio frequency (RF) transistors (DUT) in the frequency and time domain using Load Pull (see ref. 1). Load pull is the method by which the load impedance presented to the DUT at a given frequency is changed systematically (tuned) and the DUT performance is registered, with the objective to find an optimum tuning condition for certain overall performance objectives. The objectives may be maximum power, maximum efficiency, linearity or else or a combination thereof. The same is valid for the source side of the DUT. Passive (slide screw) tuners (see ref. 2) are used to create the various impedances presented to the DUT for frequencies above 100 MHz. A typical test setup is shown in FIG. 1: a signal source (1), in this case the source is internal to the vector network analyzer (VNA), (9), injects RF power into a DUT (3) via an input tuner (2) which synthesizes the source impedance presented to the DUT. An output tuner (4) generates the load impedance and is terminated with the characteristic impedance Zo (5). The injected and extracted power waves are detected using bidirectional couplers (10, 11) and measured by the receiver (9). Typical receivers are Vector Network Analyzers (VNA), see ref. 7. Such receivers can both (a) generate signal (1) and (b) detect harmonic signal components through the couplers (10, 11), in which case a reverse Fourier transformation allows creating the real time dependence of a non-sinusoidal signal entering and/or leaving the DUT. In case of an active or hybrid tuner, which cannot be fully and permanently and accurately calibrated, because of nonlinear behavior of the used feedback amplifiers, which may change during tuning, this test setup, instead of a simpler setup using only input and output power meters, is mandatory, because it also allows measuring “live” the source and load impedances presented to the DUT. The entire setup is controlled by a PC (6) via digital communication (7) with the test instruments (9) and the tuners (8). Data are collected by the PC as a function of the impedances generated by the tuners and saved in load pull measurement files.
Impedance tuners are used to create the test impedances used in load and source pull testing. Some tuners use the slide-screw principle, (see ref. 2) or electronic components, such as PIN diodes (2), see ref. 3 and 4. In this case an array of electronic switches (PIN diodes), distributed along a transmission line (micro-strip as per ref. 3), when switched ON and OFF alternatively, in various permutations, creates a multitude of reflection factors covering a large portion of the Smith chart over a certain frequency range. By placing the diodes strategically spaced along the transmission line (see ref. 3, FIG. 1, column 4 lines 47 ff. and column 5, lines 1 to 22), the combination of the individual reflection factors can generate tuning patterns (i.e. the complete cloud of points (32)) on the Smith chart (31) as shown in FIG. 3 (see ref. 3). The regularity and density of electronically tuned points depends on the number of diodes used, whereas the limitation in maximum reflection (uncovered area (30)) is due to losses associated with the used prior art micro-strip structures and diode losses. In total 2N different reflection factors, corresponding to the possible tuner states can be generated, whereby N is the number of diodes.